1. Field of the Invention
The present invention relates to a color cathode ray tube and a method of producing it, and more particularly to a color cathode ray tube in which fluorescent substance forming a fluorescent substance film on an inner surface of a glass panel is coated with a layer having a wave length selective characteristic and a method of producing it.
2. Description of the Prior Art
Conventionally, the color cathode ray tube has been used in color TV, color display and the like. In the color cathode ray tube, a fluorescent substance film is formed on an inner surface of a glass panel. In the fluorescent film, respective patterns are formed for green, blue and red with a predetermined positional relations. On an electron gun side of this fluorescent substance film, attachment is made of color selective electrodes, such as shadow mask or the like, left a predetermined interval therebetween. By this structure, it is adapted in such a manner that electron beams corresponding to green, blue and red are applied onto the fluorescent substances for respectively corresponding colors on the fluorescent substance film, and a light emission is performed.
Generally in the color cathode ray tube, non-luminous absorptive substance such as graphite or the like is loaded between respective color fluorescent substance luminous pixels of green, blue and red (hereinafter referred to as G, B and R) in order to improve contrast which is a basic performance as an image display. This non-luminous absorptive substance film is called black matrix film (hereinafter referred to as BM film). Further on a whole surface of the fluorescent screen which is opposite to the display surfaces a film is formed for reflecting light in the form separated from the fluorescent screen. This film consists, for example, of aluminum film and will be called metal back film.
As described above, contrast is one of the important characteristics of the color cathode ray tube. This contrast is a characteristic which is determined by a ratio between brightness and external light reflection of the fluorescent screen. As a means for improving the contrast, it can be considered to increase a current amount of electron beam from the cathode or raise an anode high voltage. However, this method is not preferable because power consumption of the cathode ray tube becomes large.
Further, it can be considered as another method to increase a light emission performance of the fluorescent substance and a light transmittance of the glass panel. However, the light emission performance of the fluorescent substance has already been at a high level. Further, the light transmittance has almost reached its limit in the glass panel. Thus, it is difficult to improve these characteristics.
A method of lowering a reflectance of the fluorescent screen is disclosed in Japanese Unexamined Patent Publication No. 8-7800 (hereinafter referred to as prior art I). In the method, use is generally made of a mixture of fluorescent substance with pigments. This mixture is produced by attaching inorganic pigment particles having selective absorption property in a region other than luminous wave length of respective color to the whole surfaces of the fluorescent substance particles for blue color and red color. On the other hand, the fluorescent substance for green color is yellowish in itself and absorbs lights other than the luminous wave length to some extent, so that ordinary pigment is not used. Such mixtures exert an effective absorbing action to external light coming from the glass panel side. However, the pigments are placed on a side of the fluorescent substance onto which the electron beams will impinge, so that the pigments does not only contribute to absorption of external light but also prevents the electron beams from reaching the fluorescent substance, thereby reducing brightness.
As a means for improving the brightness and contrast, a technique for a micro-filter tube (Toshiba) has been introduced in "Electronics" November 1995 (hereinafter referred to as prior art 2). In this technique, a screen of the micro-filter tube comprises color filters (hereinafter referred to as M filters) disposed between an inner surface of a glass panel and fluorescent substance films which respectively consist of fluorescent substance of G, B, R and which are formed between BM films, and a color filter (hereinafter referred to as BE filter) disposed on an outer surface of the glass panel.
The M filters consists of respective colors of G, B, R selectively and absorb wave length regions other than the luminous portion of the fluorescent substance and so absorb external lights effectively without deteriorating the brightness, thereby improving the contrast. On the other hand, the BE filter acts as a common filter for respective colors, so that it can selectively absorb external light energy having luminosity peak, thereby achieving improvement in the contrast and color purity.
However, the color cathode ray tube described above is produced by coating the M filters consisting of respective colors of G, B, R after the BM film has been formed and thereafter forming respective fluorescent substance films at positions corresponding to respective colors. Therefore, the conventional color cathode ray tube has disadvantages in that the production process becomes complicated thereby leading to a drop of yield and that a large equipment investment is needed.